Drain won't seal to Tub

I have a simple problem that I can't fix! My plastic drain in my plastic tub needs to be sealed. No matter what I use. I doesn't seal! I've tried Silicone, Lexel silicone, and even plumbers putty to no evail.
On top of that when I screw the P trap to it when the rubber washer that is used to seal the drain to the trap it actually pushes the drain up a bit becasue of the hieght of the plumbing underneath. Its an issue but not one I can't work around.
What I really need is a way to seal the drain to the tub so that water doesn't get into and under the seal and rot my floor. I'm to the point of glueing the it together now and then sealing the joint around the drain with silicone for extra protection.

Any Ideas would be greatly appreciated. I'm leaving in a couple of days and DW is not happy without her shower!!!!

Thanks
Rich

drain

Your description is not coming through clearly. You install the drain and overflow to the tub FIRST and then connect it to the P trap, or at least you assemble it to the tub, then place it into the P trap and make the final connections. If the P trap connection is too high you will NEVER seal it to the tub because that is a gasketed connection which means the two surfaces MUST be parallel. Silicone or putty, has a different purpose, and that is not to seal the drain to the bottom of the tub.

HJ, Sorry for the poor explanation....yeah I know what you mean. This is in an RV. The tub Drain is plastic and threaded on the outside. The Tub has a hole in it that I drop the drain into it. I then connect the P trap to that via screwing the P trap to the plastic drain from underneath the tub. There is nothing sealing the water from inside of the tub from getting under the flange of the drain.

Again its a crappy design of a system. I just thought I could get some great advice from you all once you understood my issue.

Thanks
Rich

Ok, I think I might have figured it out. My Drain is threaded all the way on the neck of the drain. Shouldn't I have a pc that threads up to that with a rubber washer on the other side of the Tub under the flange of the drain and once tightened up will squeeze the drain to the tub to a tight seal? Then I would also thread the P trap to the bottom threads of the drain. Right??

The top part of this P trap is not on my P trap now. I couldn't imagine why.
So with that its what seals the drain.

I hope so.
Rich