I looked into this a year or so back, a company called tinleytech
http://www.tinleytech.co.uk/ do a 45litre LPG tank with both takeoffs, they do diesel conversion (saves 25% on your diesel costs by injecting LPG)
Here is the email I got from their tech guy:
We have one type of tank that can provide liquid and vapour off take, it is currently only available in one size - 270mm x 884mm - 45ltr
The tank needs to be mounted either under the vehicle or in a sealed box/locker with appropriate venting as it is not possible to cove both off takes with a gas tight housing as with a standard tank.
We do not know of any regulators suitable for domestic supply which can accept liquid.
There is no problem with running the engine and domestic supply from one tank, if the tank above is not suitable, it is possible to use a standard automotive tank for the engine with a small slave (normally 6 or 10ltr) connected to it to provide the domestic supply.
Was £400 plus vat back then, which is why I decided not to bother.