A very common problem with the stock RV design is that the seals around the front of the engine are difficult to do well .. the transition from the ramp to the top of the cowl difficult and often very leaky. I lected to do a common modification to build a transition ramp from the stock flat ramps to the cowl top to give a smoothly curving surface for the air seal fabric to seat against. VAF has lots of examples (http://www.vansairforce.com/community/showthread.php?t=141528)
I built mine up with modelling clay. I found that if I heat soak it for a few hours at 80F, the stuff is nicely pliable!