If you get a tote, you do want it larger than your tanks. Considering your tanks are small, you should have no problem finding a tote that is bigger than any one of your tanks. The last thing you want to happen is to overfill a small tank and then have a mess on the ground to deal with. That's really bad, and not pleasant at all. You can always transport the tote inside your camper and when you park at your campsite, simply take it out and slide it under the camper out of the way. No problem and space is not problem that way.
Keep it clean by flushing it out after every use and it will never have smells or odors. I never use any kind of chemicals in mine, I just flush it real good after dumping. it's over 15 years old now, and still no problem. I carry mine in the back of my pick-up truck. It's always clean. I do occasionally soap up the outside, mainly to wash off mud, especially if towing it after a rain. (mine is 32 gallons - 4 wheels - with a side slide discharge that you hook a hose up to).
Go bigger! You won't be disappointed.