> We fly off a compact DG runway, and I don't want to tear up the bottom of the plane <

I don't what what "DG" is. But I flew my Wonder off of grass. I put a 1/32" plywood plate on the outside bottom of the fuselage. The plane was covered and then a strip of self-adhesive, non-skid tape was stuck on.

Keep the plane light. A .15 engine provides plenty of excitement and the plane will still have a lovely glide into landing.