how to make resin and wood flow together?

You could try by sanding the wood and fiberglass down to where each layer is flush with each other. But, this will only go so far. If you manage to pull the feat off it would look very impressive.

Also, do you plan on wraping the mdf or leave it bare?

quite simple really. if you have a router, then get a rabbet bit that will give you a rabbet of say 0.5". then you strech the fleech over the front, and staple into the rabbeted area, then fiberglass, and apply bondo, rage extreme, or whatever filler you use, sand then paint. I do it all the time,and if done properly, you can't tell that the whole box isn't fiberglass....

http://www.houseoftools.com/product.htm?pid=17387

in the illustration it shows a much deaper rabbet than you would want, you would want it about 0.25" at the most, because with the fleece, and cloth in that 0.25 rabbet it should be close to flush with the mdf top of the box.

the saint

it has worked out nicely for me in the past. simple and it gets the job done. the great part about it, you can choose how far the rabbet bit cuts out of the mdf. so if you want the fiberglass to overlap onto the mdf by 1/2" you just change out the bearing, but if you need more of an overlap, maybe you want it to grip a little more if you're worried about bigger subs pounding on it, then you can rabbet a full inch into the mdf, and glass away.

the saint