Aquarium cabinet

I'm staining and varnishing a raw pine aquarium cabinet + hood. The plan is to do quality work on the visible surfaces and do quicker/rougher work on the interior.... but as water contact will be inevitable, i would like to put tough coating that protects against water damage both inside and out. what is the best to use?

also, i plan to use pine sealer/conditioner on the visible surface and not on the interior. i'll probably just do a single coat of stain on the interior plus polyurethane varnish. i'm assuming that pine sealers and stains do nothing to protect wood from water? and that all the protection is done by poly?

need feedback if what im doing is good or not!

thanks in advance =):?