I would recommend Fischer aluminium enclosures such as those of the AKG series.In terms of the connectors:
- RJ45 for E1, obviously
- USB-B (I would actually go for full-size-B for robustness)
- SMA for GPS Antenna connection
Not sure if we need anything else. If there's a UART for debugging, we should of course go for the standard 2.5mm osmocom jack.