DEAR BOB: I want to sell my $20,000 motor home so my wife and I can make a down payment on a house or condo. But the motor home market is slow now. Any ideas how I sell my motor home to get $20,000 so I can buy a house? Ed R., Fairfax.

DEAR ED: Don't sell that motor home. Trade it as your down payment on the house or condo you want to acquire. You'll be surprised how often it's possible to trade something you don't want -- such as a car, recreational vehicle, vacant land at Swamp City, a vacation cabin or a mortgage you own -- as down payment on real estate you want to acquire.

The surprising thing is that the real estate agent, especially if he works independently or for a small firm, will often take your trade-in as his sales commission. This technique works especially well if the home seller doesn't need much cash and is highly motivated to sell.

If you can sweeten the purchase with a little cash (it's called "lemonading"), chances of the seller's accepting your purchase offer are increased. You'll never know if your motor home will be accepted in trade for the down payment until you start making purchase offers. The more offers you make, the better your chances of success. Today's home "buyer's market" is a great opportunity to buy before prices go higher.

DEAR BOB: We will be buying a new condominium near Miami as soon as construction is completed in a few months. As we will be paying all cash, do you think we need title insurance, too? Mrs. H. H., Fairfax.

DEAR MRS. H. H.: Yes. Buyers of new condominiums especially need title insurance. New construction offers very high risks of mechanical liens if the contractor didn't pay all his bills. Every property buyer should get an owner's title insurance policy.

By the way, why are you paying all cash? That's foolish. You'll be better off taking the biggest available mortgage. Among the reasons: You repay the loan in cheaper, inflated dollars; there is an income tax deduction for the interest payments; and the property will be easier to resell if it has a big, assumable mortgage.

DEAR BOB: Recently you said we are in a "buyer's market" for home sales. Does this mean it's not a good time to sell? I ask because my husband recently died and I want to sell my big old house and move to a smaller condominium where I won't have to mow the grass. I am 74. Maybelle N., Arlington.

DEAR MAYBELLE: A "buyer's market" means there are more houses for sale than there are qualified buyers. The reason for this imbalance is the high cost of new mortgages.

If you don't have a need for a large amount of cash, it's an excellent time to sell since you can offer seller financing to your buyer.

With a reasonable down payment (to use to buy your condo) you can finance your buyer's purchase. That should make your home easily salable. The installment payments will give you extra retirement income.

DEAR BOB: You're always writing about innovative finance ideas to avoid getting a new, high-cost home mortgage. But in our town, the realty agents think creative finance means the buyer assumes the old mortgage. Where can I find a realty agent who understands modern finance methods so I can buy a home with a small down payment? Jarvis T., Bethesda.

DEAR JARVIS: You hit the nail on the head. A January 1981 National Association of Realtors confirms your report. The survey shows that most Realtors are not using new creative finance techniques to sell homes.

There's no easy way to locate realty agents who understand innovative finance. However, when you phone about homes advertised in the newspaper want ads, ask the agent this key question: "What financing are you offering?" If you inspect only homes that are offered with seller financing, you'll probably find agents who understand how to sell homes today.

DEAR BOB: I recall that when I owned my house the mortgage company required me to have fire insurance, I sold that house and bought a condo last month. At the closing, nothing was said about a fire insurance policy and I forgot all about it. What kind of fire insurance policy do I need to satisfy my new mortgage lender? James W., Alexandria.

DEAR JAMES: None. The condominium owner's association has a master fire insurance policy on the entire structure. A copy of that policy was given to your mortgage lender at the time you bought your condo.

However, you should buy a condominium owner's insurance policy on the contents of your condo.