Teaching calm is very easy to do and dogs tend to pick it up pretty quickly.
For want of preventing an argument you can train in a pen, crate bed or mat it doesnt matter which 
The idea is to make the bed the best area ever - the dog needs to imagine it is a beautiful tropical island!
Put the bed between you and the puppy, when they show any interest in the bed put a treat into the bed.
Do this a couple of times.
Then wait - most puppies/dogs at this stage will move into the bed to get another treat. The minute the dog goes into the bed treat. Put the treat on the far end of the bed so all the dogs body is on the bed.
This is the important bit _ Throw a treat away from the bed with a release command (I use "Ok") . The dog moves off the bed to get the treat
98.9% of dogs will then turn and return to the bed to get another treat, so reward them when they go back to the bed. If the dont go back to the bed pop a treat onto the bed and they will do so.
As they get used to going onto the bed - slightly withhold the treat and they will probably sit and eventually go into a down start to only reward the down position.
Do remember to reset at intervals by throwing a treat off the bed and release with marker word.
Basically that is the principal. Over time you can increase the distance from the bed and the length of time between rewarding or being on the bed.
No stealth boast but I have an 11 week old lab puppy who will now happily stay in his bed for the duration of our supper time. He is rewarded at random intervals but he is extremely happy to stay in the bed waiting for the treats.
With your lab I bet he gets it in days. You can then transfer the behaviour to quiet times in the evening when he is lying on his mat, or if you go out to meals in pubs etc. Wellworth putting in the effort to teach this behaviour.
Use one of his meals to teach this behaviour and in a week you will have it sorted 