kribs and bristlenose would be ok with a 50mmx50mmx150mm ish cave, bn's with a front closure on with a 15mm square opening but kribs may need a slightly bigger opening on the front closure maybe 20-25mm square opening
i can do 2 of those caves for £5 plus postage at cost
postage will be around £4.50 due to the weight of the caves
let me know if you want them as im making some caves on sunday so i can make yours at the same time
thanks for your enquiry
tony