you probably should have posted a link
http://www.horizonhobby.com/Products...ProdID=HAN4100 so people were clear on the plane, I had to look it up myself to see it was a low wing sport model.
what I would do is check the firewall for triangle stock in the corners, if there is some which most H-9 planes come with now, because of repeated complaints of firewalls ripping out don't trip just assemble it,and have some fun.
if your worried about it, then warm some epoxy,by heating up some water and setting the bottles in it with the tops removed,just like pancake syrup,warming the 2 parts separatly will allow the epoxy to thin and spread out easaly.
it doesn't need to be hot just warm, it will be watery, the heat will make the epoxy kick faster so just mix a little at a time, and with a cheap brush coat the tank area with the epoxy, it will provide a fuel proof tank compartment in case you get a leak in your fuel tank and will strenthen the joints where the firewall joins the fuse other than that your just adding weight which for that plane is no help,you don't need alot just enough to wet the wood, it will provide strength and fuel proofing without adding alot of weight.
if your going to strenthen any area I would look at the landing gear attachment point being a tail dragger thats a area that can be a weak point,and on the pulse it doesnt look all that strong from the photos on Horizons site just take a look if it looks sound then don't bother with it .
finally when your coating the tank and LG areas, before you apply the epoxy, install the blind nuts for the engine mount, and landing gear first , just dip the bolts in Vasaline/petrolium jelly to prevent the epoxy from sticking.
screw them into the blind nuts to protect the threads fom getting clogged up with glue,not too deep, just enough to protect the threads, the epoxy will hold the blind nuts in place,if you coat the wood before you install the blind nuts the points won't be able to penetrate the wood to hold in place when your ready to mount your engine etc....
when the glue is dry just back the nuts out wipe any exess Vasoline off and assemble away.