If it is a permenent rest, then build it just like a sit down bench rest with higher legs with adjustment and of light materaial, that way you have an elbow rest and can use your benchrest stuff with it....

I have a portable affair made from 4" plastic pipe with a big base, it is a post affair with a bag on it..one pipe within another and holes drilled so it can be adjusted n one inch acruments with a bolt run through the holes...the top is a 4inch piece of pipe cut in half with a bag in it...One of these days I will put a table on top of it or at least an elbow rest..but for now it does well at 50 yards for sighting in and group work...and it packs in a care easy...Problem is I lent it to someone and can't recall who!

Oh well I can whip up another in aboutn 30 minutes.