Hi all. have been a lurker for a bit.
I have a 2001 Ranger XLT with a bedliner
Ordered and its arriving tomorrow.
Really need to clean out the rear seat area

I know I will need to drill through the bottom of the box and into the bed, but how best to secure it and also keep any water from getting in?
What size bolts should I use and type?

 

3/8" or 1/2" carriage bolts, about 2"-3" long, stainless steel, so they don't rust

Or regular head of the same size.

just two are fine to hold any box

You will drill the holes in a VALLEY of the bed or bed liner, because you will be putting a nut on it FIRST before the box goes on.
So the bolt goes up from the under side of the bed and then the nut goes on and is tightened up tight, so you have two studs sticking up inside the bed, how much they stick up is up to you and the box you are using.

Drill two holes in the tool box for the studs
Now..... you could use a nut on the stud before the box goes on, set at the right height so when tightening up the nut INSIDE the box it has something to tighten against so doesn't deform the plastic tool box.

Since box and bed liner are plastic I would use larger washers

And stainless steel, all the parts, for just two sets it won't be that expensive
2 bolts
8 washers
6 nuts

You can put some RTV or similar silicone in the hole thru the bed

And as always, "measure TWICE, drill once" lol

And just as a heads up, some tool box lids and hinges need clearance on the back side to open all the way, nothing worse than opening the lid and going "DOH", should have moved it 1" toward back

 

Thanks for the advice.
I have the box in the bed now. will work on securing it this weekend. Have it held in place for now with a cargo bar.
Including a pic with what "valley" I think I will drill in.
should not hit any vital things below when drilling ya?

https://1drv.ms/i/s!AlIiO3jqzK_hlVbk4Y0Gbybc1xcU

 

You are there I am not..............I know, very profound, lol.

Anyway you will need to measure, generally there is nothing outside the frame rails under the bed, just the leaf spring hangers, the closer to the edge the better.
Also keeps them out of the way when tool box is removed