Personally, being somewhat mechanically able to work on units, I wouldn't touch it, having set that long. Too much can go haywire by setting, let alone useage. Seals crack, gaskets falter, oil drains from bearing, hoses dryrot. Naw not me, I don't mind working on them but if I have to work on one, it would have to be something worth putting the money in. You can fix one thing and 5 others develop. But that's me not you. You have to do what you think best. No one can make up your mind for you, and shouldn't try. I only spoke for me and no one else. Also, sitting that long 1=st things you will probably have to replace tires and brakes(calipers, if they have them) and vaccuum lines, fuel pumps and probably even drop fuel tanks and flush. Did this on many an old car and truck while restoring. Motorhomes are altogether a different venue. Fridges, heaters, waterlines, (did they freeeze) You are talking major undertaking.
But again it's all up to you not us. All said this is only MHO