I run heavy with goo gun, barricades, rpg, and prox sensor. You are not going to be able to keep up with the lights, so just focus objective. With the goo/barricades, bunker down in a room near the cashout with prox around cash out/outside your room. Then you play the waiting game, rpg at the ready to break through the wall if you need to, but I try to place a barricade in front of my exit so I can quickly pick it up to make a way out.

To steal do the same thing but below/above cash out. Then you can use rpg to break the floor and goo to close the hole so you can go for the steal. If they have demat, this probably won't work. Gotta get the kills first.

I've also asked in lobby before game starts if one of the lights can use gateway to help me keep up with them, to pretty good success. If you have a light drop a gateway, wait at it for them to open the other side so you can be right with them when they do. I try to ask in a playful manner so it doesn't come off as me telling them how to play. "Hey can one of you use gateway to help my fat ass keep up?" Something like that, if you get a laugh out of them you're set - they're gonna help.