Sounds just like the seat bases on my '76 Doug.
Easy lift out and room for a few tools. have a feeling I left a small (cheapo) 1/4" drive socket set under the passenger seat when I sold the car frown

Graham (G4FUJ)

Sold L44FOR 4/4 Giallo Fly
'11 MINI Countryman Cooper D All4
'90 LR 90 SW