Here's a link to one I built for a friend a couple of years ago. The texture issue was solved with cloth-backed sand paper. If you need some, I'll send you the roll for the cost of postage. There's probably still 40 feet of it left.
Hawk, you could also use a pulley and some weight to reduce the weight you are applying to it (rig to harness). My pro trax (couldn't find my cheaper pulleys) lives in my home gym now that I have added a hangboard to the doorway pullup bar. Throw a few slings on that, keep the toothed part of the pulley open, use some old beater rope to have a kettlebell as opposing weight, and boom...my weaksauce is somewhat remedied.
Basically it allows you to gain the requisite strength without needing the requisite strength from the get-go.
Except for that I was an idiot and the stoke was too high so I did a bunch of hangs on too-small things without the counter-weight and now have a bit of soreness in one of those fingers...doh! If only I could have an IQ as high as my stoke...
Dude. Just use your hot wife's yoga ball under your feet. work on the core AND your hand/finger strength at the same time. Just might want to have someone spot ya or rig up something for your harness for safety though. Don't want to crack the back of your dome on the concrete.
the kid and i have exposed horizonal rafters in our fish camp cook house,and the test is to grab/pinch the bottom and just hold on ,at all,,anyway as some kind of indoor device keeps us all alittle more motivated, and wood is easy to work with ,i;ve tried a few,,try an angle grinder to create some texture and grainey surface for better ,user friendly grip,,let me know how it works,,keep on jambin,