Dean,
I'll help out, tell me the cost per day. of your static caravan location. I've a caravan, so I know a little bit about site fees and stuff. Is it static or is it stored?
Just give me a daily figure. No don't; let's assume it's £15 per day. If you do ten days work from your caravan; and that's WORK not mixed with pleasure, then you should be able to claim £15 x 10 days = £150, plus travel costs as an honest basic claim.
I reckon you can't claim for food but could claim for Personal Individual Expenditure (PIE) which many companies pay their employees when they're made to work away from home (including the Army).
This is to cover the extra expenditure you incur for working away from home; such as extra laundry costs; the cost of an extra newspaper (because your Missis will be buying one while you're away; so that's two newspapers) and the cost of a phone call home. I reckon that's worth about £3 per night. This is probably dodgy ground, but arguable if you're ever investigated.