For the enclosure I designed it in Fusion 360 with plans to screw the thing on the wiper motor itself (hence the 2 holes for the screws on the wiper motor housing). In the end, there is not enough access to fit it there and I put it under the dash. It's virtually invisible and keeps the stock look of the MGA (no extra components in the engine bay).

It's a two part, snap fit enclosure.

Fitted under the dash without the lid :