Mr Meyer,

You want to make sure the fuel tank is very secure. I have never seen that plane with the wings off so I do not know if it has its own hold built in for the correct tank.

Lets say it does not.

I do not think velcro is a good idea but I suppose it depends on how its applied.
I would look for a way to secure it with a light ply strip.
Do use the foam around it whatever method you choose. One of the things that does is keep the engine from vibrating the tank so much. You want to isolate it from all sides of the plane if possible. That is one reason I do not see velcro as a viable option.
Vibrating RC fuel causes foaming....air bubbles....problems.

You can probably pack it tight with foam then you need to secure it from sliding back with something sturdy. It will be heavy when its full, you do not want it sliding back and tearing or dissconnecting a line. Not to mention having your center of gravity go crazy.
I promise having your CG change in flight is no fun.

I bet you can download a manual for that plane if you look...or just find the PDF, save the page for reading and save your ink.

Good luck
Michael