I usually use a very thin film of blue or black RTV myself and don't have issues with leaking. Given a new pan, you should have less of an issue, but gasket leaks for covers is usually because the bolts have been overtorqued and the bolt holes are dimpled away from the head of the bolt itself. I always check that they aren't, and will dimple the holes the opposite direction by placing the edge of the pan on a 2X4 and using a bolt one size larger than the hole to bend the hole edges back towards the bolt head side of the cover so the pressure transfers to the rail of the pan vice just at the bolt holes themselves.Also, make sure both surfaces are extremely clean so the RTV sticks to the metal and not have any fluid contamination.
I always wipe both surfaces with laquer thinnner to ensure that there's no oil present as that will kill the seal. Then use an inch# torque wrench to I think maybe 16 in lb, but check that figure. Most transmissions seem to have at least one persistent drain which will keep running fluid across the pan surface for days. That one you deal with by wiping it back as far as you can, wiping the pan surface with thinner and slapping the pan on before the fluid runs across the pan surface again. You will have put the RTV on the pan before the final wipe of the transmission surface, being sure to circle around the bolt holes on the pan.
Most RTV is trans fluid resistant so that's not usually an issue either.