If I remember correctly, there are a couple of sets of plans for shooting benches in the back of Jim Carmichael's Gunsmithing book.  One is made of heavy lumber, and the other cast of concrete, which wins hands down for stability (and permanence).

Mine is only sorta permanent...I had to make it moveable in case I need to use the old road to access the back side of my property.  I used pressure treated lumber for the top, which sits on stacked concrete blocks.  It's pretty solid, but can be disassembled and moved with a bit of effort.

Greg

A few random thoughts...

1) Mann's "Gibraltar" is shown IIRC in "Bullet's Flight" and perhaps a couple of other places.
2) the NRA has several sets of plans in various reprints.
3) Our local club cast up tops out of concrete and put them on top of bases built of cinder blocks.

This last is my personal favorite even though I was not in on the design or building of them.  They beat ANYthing I can imagine building out of wood, on the other hand, they don't move very well!    If I were building one for myself and had no intention of having to move it, this is what I would build, under the scenario you describe.  Of course YMMV!! 

Froggie

Have built a number of them, in several styles and materials. I have only two specific suggestions, but these are based upon practical experience with most of the differing designs and are very firm in my mind.

Heavier is always better. Doesn't matter if it's concrete or steel or wood (I've been successful with all three), heavier is always the way to go.

Use only the 'U' style design and avoid the 'T' shape like the plague. A shooting session at each will soon reveal the advantages.

Everything else will vary with personal size and preference, but the above two suggestions remain paramount in my mind regardless of any other considerations.
Good luck, Joe