In my opinion, base building is completly out of the question but light field fortifications like trenches or MG nests could be implemented.
Also towed guns, especially anti-tank and anti-air could have some kind of system were you can dig-in and provide better protection for those.
Fortifications, I mean those that are already in the map, for example atlantic wall bunkers could be in the map and you could man the bunkers to defend the beaches or you could go for a "japanese strategy" and let them in and use your men to ambush the enemy in the land.
Also towed guns, especially anti-tank and anti-air could have some kind of system were you can dig-in and provide better protection for those.
Fortifications, I mean those that are already in the map, for example atlantic wall bunkers could be in the map and you could man the bunkers to defend the beaches or you could go for a "japanese strategy" and let them in and use your men to ambush the enemy in the land.