Hi Conor
Sounds like a nice deal. You never mentioned the price!!!
Check if the RNLI will do a free safety test on the boat for you.
Main issue is the quality of the grp / gel coat. Look for any repairs. Borrow a skateboard if you have to but get in underneath and look. Look for repairs inside the boat including where the cuddy is attached...
Poor handling can lead to bangs and cracks when a large engine is being dismounted.
Another spot is where the engine brackets are located, around the battery 'hold' etc. Often you can see where water has collected because of the staining - ask yourself: how did it get there.
On the fibreglass, look for spidery cracks (a bit like crackleur on old oil paintings) which comes with age. Look for weeping seams, particularly where something has been jointed onto the boat e.g. keel strip, railings, or where a transponder / transducer has been attached to the boat.
Check the seals on the windows! Check the hinges on the doors if any (sorry not familiar with the sea hog that much).
Check with the manufacturer and see if you can figure out how old it is - if you have a serial number it should be no problem (so long as it is the right serial number!). I think Mike Thrussel has written up a trial on them.
Too heavy a set-up for me (looking for a coastliner), but sounds very nice.
FWIW...