that's interesting zirca, i am currently umming over the same problem as the OP. I currently tow my single ifor with a 7 seater car, legal, but noit great, and i no longer need 7 seats on a daily basis (one child at uni, next off this autumn). Am contemplating buying old landy and tiny car (i do a lot of driving) or horsebox and tiny car. Really cannot decide but think the advantage of never being stuck in a field, and being able to use landy in bad weather is swaying it for me. Also dmare is a total madam and is highly unlikely to stand nicely on a box anymore than she will stand on the trailer once we arrive at an event. however nice to avoid the hitching up hassle, easier to park in small spots, quicker to go out in the evening after work in a box.
We have had both and would not go back to a horsebox. The living was fab and it was brilliant on the motorway or to take more than two horses, but cost several hundred each year to get it through the plating, then there was the time it was off the road while those repairs were done - sometimes several months. A friend of mine bought a new box on a two year old chassis and she still had problems so no way round that! The trailer we can maintain ourselves, has no mot and is easy to deal with. 4x4 handy in bad weather and gets the trailer out of even the muddiest of fields!
I compared all the costs about a year ago when we bought our Jeep and Ifor. Really not much in it. I'd only get a BIG lorry with living - the living is FAB but our good friends have one so we can use theirs when we go hunting. I prefer having the Jeep and trailer personally - did a rally today and unhitched the trailer, left dd there for 2 hours and went shopping in the Jeep :-) Also when hunting then a trailer takes up much less room.
if I was doing anything other than basic transporting or endurance I would have a lorry over a trailer every time. Nothing like standing in the pissing rain all day or getting changed with a howling wind blowing through the trailer to spoil a good show. but then again, I can't cope without the fridge/central heating/toilet and tv when I go away, so I'm probably not a good example :0)
This is something we've faced over the last year. We'd always towed an Ifor Williams behind Hyundai Santa Fe and not had a problem. As you say it was great for getting on and off show grounds and was excellent for unhitching/crewing when we did endurance.
However as DD is now 10 and we go to bigger shows for longer we decided we needed the comfort of a proper living even though we are usually only shipping one or two ponies.
We bought a 6.5 tonne older chassis (rather than 7 because it was smaller and cheaper to run) and had the body hand built to our spec ie forward facing with decent living inc sleeping for 3.
Not yet had the benefit of it (and have issues revolving round leakages caused by bad sealing of the Luton etc) but once we start going away for long periods we hope we've done the right thing. DD is very happy at least!
Now plan to change Hyundai for smaller car although I like it being a 4x4 for going to point to points etc and has been brilliant in this bad weather!
You can tow two fairly sizeable horses in a trailer, plus if you get a pick up like mine, you have huge amounts of storage. I also think generally, having a 4x4 is more practical with livestock - just things like getting water/feed to them in awful weather is easier, though this may not be a problem for you.
I think I would only consider a lorry if I had more than two horses. I'm not convinced of the savings of a lorry plus runaround over a 4x4 either.