This question is fine Valorus, Welcome to the forum! So you want to be able to train troops without a castle or town? Well, combat is one method; going to the training camps and dueling is another, doing quests for people are a good way for your heroes to upgrade. But until you do have a castle or a town in your name, boost up your trainer skill to at least level one to give your troops experience overnight. In 3.0B when you earn a castle or a town you get reinforcements based on the population of your villages.
You can also buy a barracks, Practice Range, and Stables to let your troops upgrade to new levels. Though there is a max level to doing so for each troop. Your lower level troops like recruits will upgrade to acceptable levels but not to elite levels. In 4.0 I've improved this system much much further (and fixed the upgrade pathing). I'll also end up adding mercenaries in the mix, and town population will have some greater involvement in the recruiting of troops.