Hello all 
Taking over a round soon, that has been accustomed to Hot WFP cleaning, via a shower unit, and LPG bottle, for past few years.
Can anyone help me with the following questions ? Please:
1) Who (I am in Sheffield) offers a service, to hook up the shower unit to my van diesel tank?
2) What approximate cost would this be?
3) Roughly how much will it cost to run the shower unit
4) Is an LPG bottle safe? and how should it be housed please?
5) Is LPG a lot cheaper?
6) If I want adjustable temperature, and reasonably fair control over it, what shower unit would you recommend please?
7) What is the best window cleaning hose, that is not only sturdy enough to withstand the odd car going over it, but suitably heat resistant??
Thank you 
very much everyone
I agree with SeanK on this one.
But your questions are confusing. Why would you want to hook a shower unit to your diesel tank if you are mainly asking about gas?
You can see the cost of a diesel powered unit from Purefreedom on their site. Phone Purefreedom for a quote on fitting. Maintenance and running costs are expensive on a diesel heater, but they are the safest option. They work well using road diesel but soot up very quickly using red diesel (which you are legally allowed to use in the heater only - so would need a separate fuel tank) which will increase servicing costs. Look on the webasto website (UK headoffice is in Doncaster) for an agent near you in Sheffield. They will help you with servicing pricing costs.
If they are used in a stop start environment then they also carbon up and use a lot of battery power every time they start up.
Do a search on the boat forums under Webasto heaters - their diesel heaters are also subjected to issues you are likely to experience in our wfp application if you use red diesel.
Diesel heaters heat up an internal water 'circuit' which includes a heater exchanger. On the heat exchanger is a TMV regulator valve which you use to manual increase or decrease water temperature to your hose.
When I asked A Plan Insurance brokers (Aegis Insurance) they had no issue with a gas bottle in the van provided it was secured properly. In compliance with traffic regulations, the gas bottle needs to be turned off each time you move/drive the van.
I would consider an lpg vapour tank that can be filled up from some garage forecourts. These can be fitted inside the van but the filler most be outside. However, the era of LPG conversions to 4 x 4 petrol engines seems to be tailing off so I can see more forecourts dispensing with Lpg as demand drops. (Our local garage who used to sell LPG doesn't anymore for this reason.) LPG at the forecourt is cheaper than exchange gas cylinders.
Many have used the cheap tankless lpg water heaters with great success. They are cheap and reasonably durable. They have a frost drain for use in the winter, although Spring do a controller than will activate your pump for 10 minutes when the temps drop to 2 degrees, but you must have a bypass in the van to your tank.
With this application many put the heater on their back door and vent to the atmosphere (door open) when using it. If you have it linked to a frost stat from Spring then you need a roof vent.
http://www.ebay.co.uk/itm/FASTAR-Tankless-Propane-Gas-LPG-Instant-On-Demand-8L-min-Hot-Water-Heater-/351378290157?hash=item51cfc735edThere are several different names out there but there all appear to be made but the same Chinese company. They seem to be pretty reliable. They need to be lpg heaters and
not natural gas heaters.
8 litre per minute heaters do work with a slightly higher flow rate, but the 12lpm heater won't.
These lpg heaters don't come with a gas bottle regulator and gas supply hose so you will have to source that yourself. Any caravan supplier outlet will have what you need.