Summer vacation for millions of Americans means enjoying the great out-of-doors while eating and sleeping in the equivalent of a mobile closet. People whose homes may reflect a generous sense of space willingly stuff themselves into vans with little head room, boats which boast that they easily sleep six (good friends) and tents that may squeeze three into a 5'x7' space. They do it for the sport, for they joy of being in the great outdoors and in the hope that they won't have to spend much time in them.

Designing comfortable but confined vacation living spaces is a challenge that requires the reduction of life's necessities and amenities to the minimum. Standards vary according to the kind of shelter and the needs of the user. Here are some interesting solutions to the problem - some straight from the manufacturer, others adapted by the owners.

Camping out has become an elaborate sport with equipment and facilities ranging from a simple pup tent to an elaborate motor home. For those who want to camp in comfort a popular tent is the Sierra Designs Octadome pictured here. The colorful tent weighs about eight pounds, sleeps two or three good friends and provides good ventilation. The series of flexible poles make it easy for backpacking. The overall design is a little unusual but livable.

At the opposite end of the spectrum from the Octadome is Lucia and Rob Quinn's GMC Mobile Home. "Whn we bought it [in 1975]," recalls Lucia Quinn, "we thought we would take it on long trips because my husband was thinking about retiring, but we found it so ugly - all that plastic and phony wood, we just had to do something with it." The couple drove their problem right to the doorstep of designer Carol Peress. The result is impressive. The orange-fronted cabinets were covered. The banquette (convertible to a bed), formerly a large flowered pattern in brown, orange and gold, was recovered with fabric handloomed in Nantucket. The original dinette was removed, and a double bed, covered with Dutch wax batik, substituted. The new interior, the antithesis of its origins, is a cool, summery, natural environment that happens to be on wheels.

For a time, Rob Quinn, a clinical psychologist, used the home as his office while a more permanent one was being built in Reston for him. "He really did have a couch and traveled to his patients' homes," recalls Lucia.

Alas, though, the Quinns' RV gulps a gallon of gas every 10 miles, rendering it less attractive in these gas-short days.

The art of creating usable spaces out of tiny nooks and cranies has a long tradition in boating. The "captain's bed" has entered the bedroom of many homes because of the clever use of drawers below the mattress for added storage.

For years, sailboat architects concentrated on the design of the boat from the point of view of ease in handling, speed, and general seaworthiness. More recently a new element was added to the equation - creature comforts. Today most boat ads boast expansive views (photographed with wide angle lenses) of cabin interiors and sketches of boat layouts. Variations in the placement of the galley, the head and the berths are crucial to the stability and sailability of a boat. In addition to a captain's bed, boat designers must whittle stowage space out of every area of the boat and design it for easy access and minimum breakage and disruption of the contents when the boat heels over as it is tacked into the wind.

The main cabin of most sailboats has a table, often a dropleaf "Murphy" arrangement attached to the bulkhead. Some have a surface that sits on a pedestal that can be lowered to form part of the bed. A third variation is a table with two drop leaves that rests in the center of the main cabin. Settees turn into beds at night, and a "V-berth" forward provides some privacy.

Most of the sailboats under about 36 feet on the Chesapeake Bay adhere to two or three basic variations in layout below decks. It is the finishing details and subtle choices in amenities that make these floating closets below the waterline livable.

Stoves may be fueled by alcohol, kerosene or propane, may be portable or propane, may be portable or gimbaled. Smaller sailboats usually have an icebox rather than a refrigerator. The design of the icebox varies from a chest complete with shelves providing easy access to a deep pit that complicates organizing a lot of food for a long voyage.

The C & C 34, pictured here, which is owned by Dick and Evelyn Tager, is an example of a boat that provides a pleasant combination of necessities and amenities. Just visible in the left foreground, for example, is a chart table with a space to sit and work out navigation paths. Charts are stored in the table-top itself, much like a Colonial period portable desk.

"We took it over to Oxford for the weekend a while back," says attorney Dick Tager. "We had five on board and it was very comfortable."

Though not so elaborate as the Quinn mobile home, the carpet and crushed red velvet-lined Ford van owned by David Carter offers another kind of camping (or camp) environment. Carter's van is equipped with mirrors on the ceiling and a horseshoe sofa around a table that converts to a bed. It is elaborate enough to be characterized as a bed on wheels, but practical enough to meet most basic needs on a camping trip. Like most vans, there is no bathroom, but there is a sink, an icebox, even a bar built into the storage area. The van, elaborately decorated on its sides with Frazetta-like paintings, is designed by the owner, who operates mobile disco shows, for van competitions. In the competitions gadgetry is essential for earning points.Carter's van has an intercom so that riders seated on the horseshoe sofa can talk with the driver. The radio can also be controlled from the rear. The area above the dash has a digital clock and tachometer.

A parent might well worry if this van carried the bumper sticker, "Don't laugh, I have your daughter inside." CAPTION: Picture 1, Walls of the Octadome tent are double-thickness. Since the flysheet is an integral part or the tent, there's no need to worry about creepy creatures and bugs slithering between the ground cover and the tent. By Rhoda Baer; Picture 2, Fresh air pours in through screened vents and four screened arch windows that zip closed in foul weather. The double-thick door can also be zipped closed to keep rain out and warmth in. By Rhoda Baer; Picture 3, The Tagers' gimbaled stove and oven operates on alcohol. The guard rail helps prevent spills. By Rhoda Baer; Picture 4, no captions, By Robert C. Lautman/courtesy of House and Garden; Picture 5, The drop-leaf table in the main cabin of Dick and Evelyn Tager's sailboat hangs from a stainless steel rod that doubles as a grab rail in rough weather. The settees on either side of the cabin convert into a double bed and a single bed. There is a sky-lit V-bunk in the forward cabin that comfortably sleeps two. By Rhoda Baer; Picture 6, Lucia and Rob Quinn, seen above dining alfresco with friends, retained decorator Carol Peress to obscure every bit of fak wood and garish color in their 23-foot motor home. Peress covered phony grain paneling with natural linen and replaced the fake wood on the stove with stainless steel. By Robert C. Lcautman/courtesy of House and Garden; Picture 7, The table at which David Carter sits drops down and along with the horseshoe sofa becomes the support for a double bed. The partition is covered in crushed red velvet. By Rhoda Baer