A campervan has a fixed bed and fixed cooking and washing facilities among other things. It can be re-registered as a Motor Caravan
if it's fixtures comply with DVLA regulations, though re-registering it is not compulsory. Re-registering can lower your insurance premiums and changes your MOT class.
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/522756/converting-a-vehicle-into-a-motorhome.pdfA day van or surf van has no strict definition (at least not an official one) - It could be as nedforceone describes it above, it could have a bed or just a roll out mattress on the floor. Similarly, cooking and washing facilities may or may not be present, and may not be fixed - you could just use a cartridge type stove kept on a cupboard for example. As there is no official class for this, so you cannot re-register it as anything else with the DVLA - it remains a Panel Van.
Simply put, if it complies with DVLA regs, it is a campervan. If it does not meet DVLA regs, it is essentially a day van/surf van.
To answer your last question - really it's up to you - you can easily throw your bikes in the back of a day van, and sleep on a Karrimat on the floor and cook on a Trangia if overnighting or longer.
If you want more home comforts and a comfy bed, then a full campervan conversion is the way to go.
2011 SWB medium roof 2.2l Mk7 115 T300 in Frozen White. Stealth Camper converted.
"It's better to burn out, 'cause rust never sleeps..."