I like the idea of freighters having modules. I still want them to be slow and lacking in agility. No place for MWDs for instance.
However I think there are some freighter exclusive modules you could use. Some form of armour that provides a ‘thorns’ effect but greatly reduces cargo capacity so that ships shooting them get zapped with lightning or something. Perhaps different race freighters would cause different damage types with these thorns. Still gankable but you have to calculate a little tank with your gank and ensure you understand the value of the cargo is going to be worth it.
A tug module that lets smaller ships Web them and tow them for a speed increase. This would be mutually exclusive to the thorns effect and would mean gankers would have to pop any tugs quickly lest the freighter get pulled back to the gate and escape the gank or put enough webs on the freighter to counter the gank. So again you would need to be sure you understood the fit and tactics the haulers were going for. Plus the hauling fleets would look neat with little fleets of supporting ventures or something.
This one might be controversial but an inferno module. It doesn’t make the freighter any less gankable but when transporting materials you don’t want the enemy to have the freighter will immolate it’s cargo, however this can only be used actively so it’s about the nerve of the freighter pilot. Imagine surviving the gank and having immolated your cargo or holding on too late and giving it all to the enemy corp. the draw back to this one could also be if you don’t immolate the cargo is more likely to drop. (This drawback might make RMT a bit easier so perhaps a bad idea)
I’m sure we could come up with all sorts of interesting mechanics to make hauling a bit deeper and a bit less afk.