Good Finish?

Next to the 3' door to my workshop I'm building a removable 1' section of wall. (The shop is in the basement below a detached garage. Since I'm in the process of building the thing, I figured now was the time to put in a little extra doorway capacity, rather than taking a Sawzall to it someday -- in retrospect, I think it was probably more trouble than it was worth for one extra foot :-)
Anyway, I install and remove this 8' x 1' 2x6-and-plywood-and-insulation-and-drywall monstrosity with a big rubber mallet. To prevent crashing through the interior drywall (or the exterior cedar lap siding), and to provide a good mounting surface for the 5" barrel bolts, I made a pair of 12" x 12" x 3/4" thick birch plywood panels, one mounted at the top and one mounted at the bottom.
I could leave the panels raw and unfinished, but I figured that since I already took the time to chamfer the edges and sand the whole thing silky smooth, I should at least throw some sort of finish on them to prevent rubber mallet marks and the accumulation of grime. (Yes, yes -- I -know- it's just a shop :-)
Any suggestions? Just a simple polyurethane? I'm more interested in durability than giving the appearance of fine furniture. (Yes, I'm both a newbie at carpentry and woodworking, but the process of building the garage and shop have been an outstanding learning experience thus far.)

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