Dude easy, make the floor in the boat sit higher than it would actually be, wouldn't have to be much just 1/2" - 3/4" considering the size it will be barely noticeable unless you pull out a ruler. This will give you a tonne of room under the deck. Then just put all the goodies along the keel where the V is where the gas tanks are in the real boat , make sure it is sealed good are and your fishing. Low CG, easy to remove entire floor panel and more sealed volume in case of water comes into the deck cavity.

I moded a toy dollar store boat like this before, and if you aren't careful water gets in the deck cavity and she sits real low and/or sinks.

Cheers,