Before you cut a single panel or strip out a single screw, get the plan right. A campervan conversion lives or dies on this stage. Decide who is going to live in it, what you need, how long you'll be in it, and what climate you'll travel in. Then choose the smallest possible vehicle that will fit those needs — every extra metre of length costs fuel, money and confidence on narrow roads.
Step-by-step
Define the brief
List every trip type you expect (weekend hops, full-time, off-grid, festivals). Decide how many sleepers, whether you need a fixed bed, indoor shower, and an inside kitchen vs slide-out.
Pick the base vehicle
Most builds use a Mercedes Sprinter, VW Crafter / MAN TGE, Ford Transit, Fiat Ducato / Peugeot Boxer / Citroën Relay (the X250/X290 platform), Renault Master / Vauxhall Movano, or VW Transporter. Check L (length), H (height), payload (kg) and gross vehicle weight (GVW). For UK self-builds the practical sweet spot is L3H2 / L4H3.
Measure the shell
Take internal length wheel-arch to rear door, internal width at floor, width between wheel arches, internal height (floor to ceiling), and door apertures. Mark all factory bolt holes and seatbelt anchor points.
Draft 3 layouts
Always design at least 3 layouts before committing. Use 1:20 scale graph paper or SketchUp. Test fixed bed across vs lengthways, bench-bed conversions, and wet-room vs dry-room.
Weight & balance check
List every heavy item (batteries, water, gas, fridge, tools) and roughly position them. Aim to keep heavy items low and between the axles. Stay 100-200kg under your GVW for safe loading.
Budget the build
Typical UK self-build budgets: bare-bones £4-7k, mid-range £8-15k, fully off-grid £15-30k. Add 15% contingency. Track every spend in a spreadsheet from day one.
Order long-lead items
Roof lights, diesel heaters, leisure batteries, fridges and windows often run 2-6 weeks lead time. Order them as soon as the layout is signed off.
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Buy the kit for this chapter
The planning kit – measure twice, design once.
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8 m tape measure (Stanley FatMax)
~£18Long, stiff, magnetic tip. The one you'll use for the whole build.
1:20 graph paper A3 pad
~£9Scale-draws every layout fast. Better than SketchUp for first sketches.
Bathroom scale (component weighing)
~£20Weigh every heavy component before you fit it – budget your payload.
Site notebook + waterproof pen
~£15Rite-in-the-Rain style notebook for measurements in any weather.
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