Well guys, I have an RCV 90 SP and it does vibrate.
Actually it is a different vibration (a torsional one) from other 4 stroke engines.
After 2.5 gallons running on the bench I installed it on a World Models Super Chipmunk 60 and did some reinforcements in the firewall, but not different that I would do with any other ARF plane.
The firewall resisted very well. The problem I had was in the front wing junction with the fuselage. I had to sheet the wing with aluminum and some fiberglass.
I don’t know how long the plane would last because after six month I hit a dead tree and lost it (no, my name is not Charlie Brown).
I had a lot of problem with the muffler. I had two originals and then changed to an OS. The OS is lasting but the pressure nipple didn’t resist the heat and I had to drill and tap a bigger one.
I’m looking for a new plane to install it. The engine is worth it. Has a fantastic noise, is very economical and with a lot of power. And, of course, disappears completely in the cowling.