Rear Tub: Drain holes/Dinitrol/mat questions?

I'm in the process of fitting a new canvas to my 90. Have painted the rear, fitted the sticks and bought a new rear mat (see photo). Following some rain, water is pooling at one end and I was wondering if I should be drilling some drain holes. If so, is there any special advice on doing this such as where they should/should not go, size of hole etc. I want to take the canvas off during the summer (possibly) so the base will get wet. Also, should I be putting some dinitrol under the mat to protect the base metal? Finally, is there any special advice regarding the fitting of the mat I have bought to prolong its life. Thanks.

In my series 2 I just got a sharp drift and punched a small hole in the bottom front corner of the tub each side, sounds brutal but so long as punch sharp it leaves a nice tapered hole.

I just drilled a hole in the bottom corner of each side of the tub.

I haven't done anything special with the floor, just put a rubber mat which I periodically take out and clean