I would pass on Rodinal if you are shooting HP5+. Too grainy and Rodinal is not the best developer for medium speed films or push processing.
If you are renting a car, I would just mix up a some D76 and fixer using gallon jugs of water and throw them in the trunk. Be sure to label them as "Film Developer - Do Not Consume"
HC110 was supposedly developed for photo journalists developing their rolls in hotel rooms around the world. It is a thick syrup and a bottle will develop a lot of film.
You'll get about 15 rolls out of a 1L bottle of DD-X.
Ilford ID-11 (D76) comes in powder form to mix 1 liter. It's easy enough to buy a bottle of water and mix up a batch to develop a few rolls at a time. A few packs of ID-11 are also a lot easier to transport than bottles of DD-X.
I've developed a lot of film in hotel bathrooms. Usually I'll wait until I accumulate 10-15 rolls and then use up a full liter of something like ID-11 and fixer. That way there is nothing to store. If I do need to store mixed chemicals I stash them in my locked suitcase. Obviously you could put them in your car if that is how you are traveling.