It's totally doable to have a saltwater tank smaller than a bathtub and still travel for work/vacations. I'm gonna go tongue-in-cheek here (a little)... you can go one of two routes:
1. Automate as much as possible. That way when you have a blip on your gfci or an ATO sensor gets stuck/knocked off the glass by a snail or whatnot you're guaranteed to get a notification of utter catastrophe while you're half a country away and can come home to a complete tank crash as the systems proceed to dump a weeks worth of fresh water, Kalkwasser or other doseable in all at once. Or it'll shut down all pumps, heaters and lighting... your pick.
2. Keep it as simple as possible. That way anyone who tells you it's too hard to drop a thimble full of food in & add 1/2 to 1 cup of buffered RODI/distilled a day can get the full measure of a well-deserved eye-roll.
In my case I went the latter route on my 9 gallon tank... it's been up and running for well over 4 years. No ATO. No controller. No dosers. Multi-day pillbox of mixed pellets to dump in the top. Bottle of top off water pre-mixed with carbonate & a shotglass next to the tank. Sticker on the side of said tank's water line with a post-it that says "fill to here". Several times a year I take trips & out-of-town vacations for 4+ days and have never come back to anything seriously out of whack. No way to make it simpler. In our pet sitter's own words - "if I get that wrong you shouldn't trust me to take care of the dog, either."
If you're frequently travelling I'd still go on the high side of your planned volume for a little added stability and the ability to stock a few more things of interest. Also, you may want look into an All-In-One system (JBJ/IM nuvo's got some really neat less expensive ones, just steer clear of the larger bent-glass tanks, shattering hazard), mainly for the lack of sump/plumbing as well as for a visually striking design. Much harder to do when the tank manufacturer has to design for holding 300+lbs of water in check.
EDIT: all kidding aside, bobz has a VERY attractive nano tank - what he says definitely will work, too. But if you're just considering getting your feet wet so to speak I feel it's good to start out with inexpensive-yet-effective approach until you get a good understanding of the basics and what the gadget-dollars can & should get you.