I had side windows fitted professionally. And paid the pernicious car tax in force at the time...
The following link should get you to a sliding window supplier
http://www.leisurevehiclewindows.co.uk/Get dark tints fitted, as these help in car security.
If you are building a camper then you could get away with just a near-side door fitting, this will help contain costs and improve vision at oblique junctions. Although the professional driver approach of just left of the crown and well out from the kerb, plus stopping square to the main carriageway, (not the Give way/Stop marking,) should help your driving safety; before you fit the window(s).
The limited vision normal in vans demands a different driving technique and too many drivers buy vans and treat them like cars, only to cause mayhem because they never learn to 'drive' using the mirrors properly...it's the first thing you get taught when learning to drive LGV and PCV vehicles.
Replace the interior lighting with a mix of Fluorescent AND LED sources. A second leisure battery is a must, the original underfloor fitting is just about large enough for starting and perhaps an hour or two of original fitted radio use. I had the 'heavy duty' battery fitted from new but it is only about 5amp/hr larger than standard enough to ensure starting on a UK freezing morning.
The standard item will not survive an extended evening of 'entertainment' if this is accompanied by LED TV and satellite dish; add in enhanced CD/DVD/FM/DAB Radio and perhaps laptop or tablet pc use. The short cut of parking on a slope and 'bump-starting' is fraught on a grassy field with the added risk of being stuck at the foot of the slope...
Standard 4x2 Rascary's are not good off-road vehicles. There used to be a 'locker diff' that suited the Suzuki SJ-410 Jeep and this might be adaptable for use on a Rascary making the standard van a little more able in slippery conditions. Those with grey imports may have 4x4 as standard... It is possible to fit tyres from a quad to a Rascary but these are not street legal and will need a suspension raise to get enough bounce clearance with the consequent interesting changes to ride and road holding/handling.
A two berth Camper will require an exterior 'extension' tent as you'll need somewhere to stand to make up stow the bed not nice to do on a damp campsite field before breakfast. There are 'zip round' tailgate tents too which means you can cook breakfast in comfort if you fit under the tailgate when it is raised.
Make sure that any furniture fitted is properly secured to reinforced areas of the floor PLUS fitting some spreader plates under the floor. The latter will require the dropping of the exhaust system AND the heat shield etc. Short cutting here may seem preferable in cost and time, but having cabinetry and its contents come loose under heavy braking really will take the joy out of your weekend breakaway.
You may also need a trailer to carry the side/rear extensions, Barbecue and fuel, dog bed, wet weather gear, surf/body-board, and anything else that won't fit inside once the bedding. kitchen, food stock, leisure power supply are installed in the van...any space that is nominally 6' x 4' is soon occupied. There are times when a 2 berth tear-drop trailer-caravan would make more sense. And fit the van as a pic-niker with an simple 'mushroom' table with a couple of seats and perhaps a wash-stand rather than a full kitchen.
IF you are a naturist and follower of Zen living then a Rascary camper may suit otherwise perhaps a slightly larger base vehicle may make more sense...
