Its not so much a puller you need, more a press to extract and refit the bearings. The puller will help remove the hub from the axle but those bearings are difficult to remove without the force of a press to help. It can be done though
Trailer Guy will obviously be better placed to advise you where you could get a press small enough to carry around and still be up to doing the job, ours isn't mobile, I remember him posting a picture of his a while back, which was perfect!
I'd be inclined to carry a complete spare hub with good bearings already in place ready to fit, then the puller will be the only "specialist tool" that's needed (sometimes you don't even need that) to remove the hub, ready for swap over. Might be easier than pressing one in on the roadside ?
Peter @ Boatsandoutboards4sale ~ www.BoatsandOutboards4Sale.co.uk
~ 07930 421007