From 1 short end of Bottom, measure and mark lines 465mm and 885mm for positions of Dividers.
Line up 1 End, flush with outside edge of 1 short end of Bottom. There will be an 18mm overhang at the back. Apply PVA, predrill, then countersink and screw through End into Bottom.
Centre 1 Divider to 1 mark made in Step 1. Apply PVA, predrill, then countersink and screw through Bottom into Divider. Repeat to fix other Divider, centred to other line.
Place remaining End flush with edge of other short end of Bottom. Keep overhang on same side of assembly as other End. Apply PVA, predrill, then countersink and screw through End into Bottom.
Turn assembly so it sits Bottom-down on your workbench, with Ends and Dividers now pointing upward. You will notice the Ends are slightly taller than the 2 Dividers. Place Top in position, resting on Dividers and butted against the inside of both Ends. Apply PVA, predrill, then countersink and drive screws in at each connection point to secure.
Apply PVA, then place Back in position on assembly. Predrill, countersink and screw Back to assembly. Do not drive screws into Top where cut-out for basin will be.
Double-checking against the dimensions of your basin, use a square and pencil to mark position of basin on Top.
Use jigsaw to cut along marked lines on Top. Remove cut-out and discard. Clean up excess PVA with a dampened rag. Test-fit your basin and adjust slightly if necessary, accounting for thickness of benchtops to be added later.
Fill screw holes with wood filler. Let dry.
Using power sander or fine-grit sandpaper wrapped around sanding block, rub over entire assembly until smooth.
Transfer assembly to drop sheet laid out in well-ventilated area. Paint assembly with primer. Let dry.
Apply 2–3 coats of chosen topcoat. Let dry after each coat. If using a spray product, allow sufficient drop sheet coverage to catch overspray.
Using a saw, cut offcuts of timber to act as temporary support legs under vanity. Stand vanity in position at desired height.
Screw through Back and 1 End (if possible) into wall studs to secure.
Apply adhesive and press benchtop pieces into position. Apply weight to top of both bench pieces to ensure a good bond or use masking tape to hold bench pieces in position. Let dry.
Have your plumber fit and connect your basin.