Based on my experience with an old Holiday with front and rear caps, the current Jayco with neither, and conversation with an RV repair shop:
Front Cap is an Essential (or on the flip side, Deal Breaker)
Rear Cap would be Nice to Have. As Ron Dittmer points out, a Five-Sided Cap (picture a shoe box lid and count the surfaces) provides better sealing AND moves stress away from the square corners. That said, the rear of the RV is more stable than a Class C overhang, and we don't drive backwards into a rainstorm.
