I doubt he will sell his properties, however, it is not uncommon for a candidate to loan his/her campaign money and be repaid with interest. Additionally, it is not uncommon for a campaign to rent out spaces in buildings they own or friends own. So long as the rent is reasonable, or the interest rate in terms of loans there is nothing wrong with this. Some candidates will loan money to the campaign and not expect repayment; or may not be repaid if subsequent contributions do not come in. There have been some issues in the past with candidates loaning money to their campaign at high interest rates. I believe Rep. Napalito of California was reported as having charged high interest rates, but I could be wrong. The reason Trump may be having a small hiccup in campaign finance fund raising right now may be due to the threat of the "conscientious objector" movement within the Republican delegates. Once this is sorted out the campaign money should come rolling in. They will need this situation to be advertised as settled sooner than later.