I have seen all sorts of high seats and prefer the modular ones rather than big one piece ones. I have found the lightweight, "portable" high seats to be rather flimsy, but I am a big bloke.
Also if you are going to put a highseat up the day before you shoot, why not put up one that is strong and will last a lifetime.
My favourites are the ones made by Paul Davies (PD Highseats) and I have looked at a lot. They will break down so I could carry them in and on my old Suzuki Jimny (and in my newer Grand Vitara) and they are strong enough to take my 20 stone. Fully galvanised and very well made they will last you a long long time. They are also very good value.
Simon