Sound out the top of your 25 to see where it is cored and where not. On my 2003, the center part was not cored, but the outer part (not raised) was cored--and you could put screws in without issues. The cabin sides, are thin. Aft bulkhead is cored. You will have to check out the thickness of the foreword bulkhead of the head. You can check that where the shower fixtures or the toilet paper holder is cut into that bulkhead.
As much as I love Starboard, It can be difficult to get it to adhere to other surfaces. I have found wood, or PVC lumber to be better ref adhesion to the side walls, and that is what I use. For example for the paper towel holder and speakers I have epoxied the wood to the side of the cabin. I mix the epoxy, and if irregular thicken it with cabosil, or use a thickened epoxy. Hot glue holds the wood in place until the epoxy dries. I have used the window frame screws in some cases, but often they are not positioned correctly for the item I wish to put on the side.