I agree. You should have something anchoring the back of the tank to keep it forward - Velcro strap, 2 #64 rubberbands, balsa block or strip. Something.

Also, with a gasser (spark ignition) it is S.O.P. to NOT use a metal throttle rod. The spark can cause an inductive interference that migrates to the receiver via the throttle servo & servo wire. You're probably OK, as the servo arm is Nylon, but it is something to keep in mind. NO servo should be within 10" of the spark plug or ignition module.

I epoxy my cowl blocks in place and once that has dried I drill 1/8" holes through them and right on through the firewall and then epoxy lengths of bamboo shis-ka-bob skewers (locally called "Spedie Skewers") in the holes as a mechanical anchor to supplement the epoxy.