we go up there a good bit, but havent found much boondocking...
we stay at the redding recreation area just east of Cass on the Mulberry River. its pretty remote and has a heated bath house and is pay on site $13. the mulberry river is nice and you can canoe in it. jasper is a cool area and the buffalo river is there and has good canoeing and kayaking. there is steel creek between ponca and jasper and there is tent camping there and trailer camping only if you have horses, but the tent area is nice and right on the buffalo river. if you happen to be in jasper...you have to get a burger at ozark cafe. its a life changing experience
we did find some boondocking around marble falls, but it was very remote and the road was pretty washboard and there wasnt much to see there. i think staying at redding or steel creek will be good for a first time and redding has the heated bath house, so thats nice if youre not set up for showering yet.