We tow a box trailer when we go to gigs with our daughter.
The fuel consumption doesn't change drastically. The equipment is approx 200 Kg but the trailer is marine ply and solid, it is braked but I'm not sure how well it brakes in real life.
I don't usually go fast in the MH, but towing means that you are speed limited anyway, a nice solid 60 on motorways, only being overtaken by cars with jet ski's, dinghys and caravans.!!
You'll know Rhuallt hill nr St Asaph, the rig only loses 5mph going up the long drag. I've got a Ducato 2.8 HDTD, just getting run in at 57k (yes, I've noticed the difference over the past 3 yrs since getting her!).
The Mersey tunnel charge is double with a trailer.
As my Kontiki has a long overhang and no rear window, reversing is almost impossible, even having a reversing camera doesn't make it that much easier. As the trailer is so much narrower than the MH, by the time i see it in the wing mirrors, it's almost jackknifed!!
Parking can be difficult, I can just squeeze into a double length car park in Asda, but end up taking 4 spaces. (Oh for the purpose built RV parking in many US & Canadian locations!!)