I have a fairly large area to fly - about a 10 acre field, but it's surround by tall trees. The field is longer north/south than it is east/west, so with a west wind, it's tight to bring it in. I can take off and fly above the trees no problem, but haven't really got the landing down very good yet. I always seem to eat up more approach then I need to trying to come in and avoid hitting the trees. I've never flown with flaps (really a beginner at flying). Will flaps make that much difference to go through the trouble of building a model with flaps for STOL performance? Also, is it possible to convert any old aileron plane to flaperons and would it be very effective? I have a Top Flite Sierra 60" trainer built and ready to fly with ailerons - would I be able to use flaperons on this plane? I've been thinking about building a Cub - think flaperons would work on that plane? Thanks.

Flaps work better than flaperons. With extreme flaperon down, your lateral control goes away, and in fact reverses.
Splitting full span ailerons into seperate surfaces; ailerons and flaps is a better choice. About 30% of the semi-span becomes a flap while the aileron response is hardly affected.
On a Cub, with barn door ailerons, flaps work extremely well.

You might want to change the landing approach. Rather than a long straight letdown perhaps a fairly level, tight, circling letdown would work and you roll level just prior to touchdown. Kinda reminds me of the Cosair landing on a carrier in WWII. The disadvantage is that the timing of the maneuver might be beyond your skills at present.

I do a similiar maneuver with some very slow fliers (5 ounces or less) in the street in front of my house but they are very slow and don't have much effect on the environment (houses, pocket book, etc) if I mess up.

Trouble getting down is often a result of a few factors. One would be the idle speed of the engine and the pitch of the prop.

First, see if your engine will run at lower idle speed. If not, you might need to give some attention to tuning the low speed mixture. At idle, you pinch the fuel line for 3-5 seconds. If the engine speeds up appreciably, you can lean out the low speed needle. That will make it run faster, but only until you change the idle setting of your throttle. Once you adjust it lower, the motor will be capable of running slower, giving you steeper approaches.

Also, you might try switching to a lower pitch, larger diameter prop. This type of prop will give you more static thrust at full throttle - and less thrust/more drag at idle. That will also help make your approaches steeper.

You might want to learn how to sideslip - once you get this down pat, you can easily make 45 degree descents at minimal airspeed, but you need a fairly powerful rudder, and lots of aileron area, if your model has a fair bit of dihedral. I experimented with landing flaps, but abandoned their complexity in favor of sideslipping approaches.

This is what I like to do...

When I fly a fun fly in high winds it is hard to get it back down to the ground simply because it will still fly when the ground speed is zero and trying to land it like that is a bit dicey. To make it come down quicker I use flaperons up. This makes the fun fly, which like a trainer has a light wing loading, come down nice and smooth without stalling.

gubbs3:...also known as SPOILERONS...

this would be the way to go to drop down fast and safe. A guy at our club has the setup on his Twist 3D and it works FANTASTIC.