To succeed at a long distance relationship takes heroic virtue. Your question represents a very common situation to have to deal with; namely, where to stay when one person is visiting the other. And when both have openly committed to staying chaste, as you have mentioned, then it seems it would be okay to entertain certain lodging options that would otherwise be an obvious impossibility under the normal rules of chaste dating.
You are basically asking if the two of you can spend the night together under the same roof. The guest rooms seems to offer a suitable protection. But there is no question that you must not stay overnight in his home and arrange to stay at a hotel. Perhaps if he had a roommate or lived with his parents who would be there, you could consider it more seriously. But his home where he lives alone is highly discouraged. Maybe he has family you can stay with during your visit. There can hardly be a good excuse for staying in a guest room of a man who lives alone. Saving money on a hotel is not as important as saving your virtue.
I would further advise that it is prudent to not be alone with this man in his own place. We have to take care of all practical things regarding avoiding the near occasions of sin as we have learned as Catholics.
I realize that there might be an age and maturity factor involved here. It might be you are both older single Catholics, much more mature and in control of your emotions and feelings. And you may have already discovered that you both are respectful, and he is a gentleman, etc. Therefore, it probably seems much more reasonable for you to consider staying at his place, and he does not think it inappropriate to invite you stay there. It might even be there are financial matters that prompt this and make it also seem practical and doable. Finally, it might be you both are seriously going to see to it that nothing happens and preserve your chastity.
I will tell you this. From my long experience dealing with single men and women, sins of the flesh are something every person is capable of, no matter how unlikely it seems. You would be surprised what anyone, even yourself, is capable of under the right circumstances.
I'm sure you trust this man, and he is well intentioned. But it is a matter of propriety and prudence that you not be alone together in a place that would allow for any unchaste temptations. Staying over night at his apartment is definitely out. Spending the evening at his apartment is also not so wise.