Very late reply here, but something in another thread prompted me to look into this. Surface-launched Sea Eagle was known as P5T.
Design-wise, P5T was apparently very close to the zero-speed helicopter-launched version of Sea Eagle for the Indian Navy.
I haven't found an actual weight, but according to Friedman's World Naval Weapon Systems , British Aerospace claimed that three P5T could fit in the place (and presumably weight) of MM40 Exocet. MM40 was around 1150 kg per canister, which implies Sea Eagle SL was being claimed in the vicinity of 800kg including canister and boosters. That seems low, since the bare air-launched Sea Eagle was around 600 kg not including the strap-on boosters.