I always await the convoy from a position ahead of it if possible. As you have already realised the chances of detection by them especially whilst you are surfaced are high to say the least.
I try to sus out their search pattern in advance and skirt around them during the day/night in preparation for a dawn/dusk attack.
The only time I'll approach them on the surface is at night and even then I'm 'decks awash'
The escorts in GWX IMO are the challenge this games been missing for so long
