Hi and thanks for contacting us. It's good that you are asking these questions before you before you buy your Hermanns tortoise, rather than afterwards.
It's not ideal to take a tortoise on a long journey, as it's a bit stressful for them, but it's not impossible either. The important thing would be to keep him in a container that is dark and is cool (in that way he won't want to be so active). You could fill the container with shredded newspaper, or even a good substrate like a sand/soil mixture) so that he can snuggle in and dig down if he wants to.
It is perfectly possible to leave them on their own for a weekend. They can easily go without food for that long, or you could pick some nice weeds and flowers and leave them in the fridge in a plastic bag and a neighbour could feed him. Regarding flipping on his back -- they can usually right themselves if they have something to push against (like a rock or a plant or anything really), but sometimes they don't manage. The most dangerous thing in that case would be if he would flip over on his back under the heat source and not be able to get upright, as he could dehydrate quickly. Many people would advise not to take a tortoise on a two-hour return trip once or twice a month, and strictly speaking they are right, but I think you could try it and see how it goes. When you get to your destination, give him a nice bath, in a container that he can't see out of, in warm water up to his chin, to rehydrate him, and that will help too.
Just in case you don't have a care sheet for Hermanns tortoises yet, here's a link to one:
https://www.tortoise-protection-group.o ... 014New.pdf
Whatever you do, don't buy him a vivarium (pet shops often try to sell you these and they are a bad environment for tortoises). Get a tortoise table (you can even easily make one out of an old bookcase on its back, with the shelves taken out), or you can buy ready made ones.
It's also a good idea to buy your tortoise from a UK breeder. They are usually less expensive and the after-sales care is better because the breeders just want to make sure that their tortoise goes to a good home (and you might even get to meet your tortoise's parents). Or you acquire a rescue tortoise (one that needs a home because his current owner can no longer keep him). We often have rescue tortoises on offer (and no money can change hands).
Hope that helps and don't hesitate to contact us if you have any more questions or problems.
Nina