Seems obvious, but let's reflect for a moment.
So.... what does a parent do for an actual baby when they are away from home and cannot be showered? Ummm, this happens every day, millions, if not billons of times across the world. If you are an adult baby and needing taken care of, well... It seems the same concept, except on a bit larger scale. Larger changing pad, larger baby wipes (and perhaps more of them), baby powder and cream, and something to contain the soiled diaper and wipees to dispose of. But the "end" result (no pun intended), is a clean bottom and everything taken care of, and a freshly scented and acceptable situation.
It is again a bit larger scale, but certainly not one that cannot be acceptably handled if you have the proper items. Having someone to actually help in this verses doing it yourself ensures a very positive result.
For me, your real concern seems to be not whether it can be done, but rather, is there an acceptable place to do it? You are not going to find adult sized diaper changing tables in most bathrooms, and doing this in the park or in a public place could end you in a not so comfortable conversation with your local law enforcement. Hence, carefully identifying WHERE you can do this away from home and a shower is a much more important consideration than the question of whether a shower is necessary.
:detective3
Teddy Bear Cowboy