The specific question of having a tent large enough to store the bike in it, that tent will weigh a lot more than a good lock. That tent will be big enough that it will take a lot of ground space to put it up.
The kind of lock you need varies greatly by where you are. Most bike touring is done in places where a smaller lock is adequate. I usually get by with a small light weight cable lock and padlock. If a place may have a high enough theft rate that my lock would make me nervous, I do not go there. Quite simply, if I am going to be nervous and looking over my shoulder, I am not going to be enjoying myself as much as I would have if I was elsewhere.
On one of the tours I did with a friend and former co-worker, he was quite nervous about theft of his titanium bike, so he followed the rule that your lock weight is inversely proportional to the weight of your bike, his chain weighed a ton:
If the reason that you bring a cot is that you can't get up off of the ground, if you crash your bike you are going to be on the ground. Seriously, consider a gym membership and diet counseling. I enjoy biking much more after losing 15 percent of my body weight, and my starting point was 205 to 210 pounds. A calorie deficit of 3,500 calories is one pound lost.