1st gen Hercu line?

I have a 1985 4Runner. I have wanted to rhino or herculine this
thing for quite some time.
I have finally decided on the "do-it-myself" Herculine.

Here is my dilemma. I want to line into the cab. So, I would line
the bed, the tailgate, the floor boards and about 1/5th of each
of the cab doors...from the floor up to where the vinyl linig stops.

However, the bed walls (and the tailgate for that matter) are vinyl
lined also.When you pull the vinyl lining attachment back the sheet
metal is not whole, i.e. gaps....between the bed wall and the
exterior fender panels...etc....

Question, do i leave the vinyl be...and just rhino line the bed and
what I can of the walls..kinda like the cab doors...or do I attempt
to put a layer of sheet metal over the existing "walls" creating a
nice new solid wall for the hercu-lining?

Do I go over the edges on the top of the bed walls?

If I dont line the walls...then rain or water could possibly get
between the vinyl lining (board) and the (what is there of
them) "walls" of the bed.

Decisions ...decisions...

Any ideas? I am not much of a welder....or sheet metal shaper....how
much does sheet metal cost...and if I can find a buddy with
welder...could we put our fabricated walls on "easily?"

Basically, it seems to defeat the purpose if I dont have a water
tight/resistant/proof bed.

I drive around alot with the top down.

Thanks in advance...
D.