Looking for the best hole filler on the inside of our RV

No silicone in walls. I'd suggest to use a resin based spackling paste. For the usual homeowner, a lifetime's supply can be bought at a Sherwin-Williams store for under $10 in one can. This material adheres well to different materials and won't crack or shrink like more common acrylic spackling. It is easy to apply and is sandable/paintable.