Where do I stay?

I am in an LDR with my girlfriend, and I am soon going to do a one-month paid work placement where she lives, which is great because I will be able to see her for all of that time. I usually go and stay with her for a week/10 days, and her parents always let me stay at her house, which I really appreciate. They are very nice people, always cooking for me, and have even bought me gifts. My girlfriend has also been to stay with me, once for a few weeks, and otherwise once or twice for a week. Since I would be staying for a month this time, I intended to find a room/flat to stay in, as I felt that they were not obliged to accommodate me for 1 month, especially since I was working, and I would not have even asked. However, my girlfriend has told me that it is really no problem for me to stay there, and they have offered this. To add further, they have a sick relative staying with them at the same time, which made me further want to find another place. My girlfriend insists that her parents have said I can stay there, and it is really no problem, but I still feel very bad. Admittedly her city is an expensive one, and I would be paying for a box room for a few hundred pounds. She works full-time, and said we would only be seeing each other at the weekends probably, if I stayed there, and she thinks there is no point of me wasting money on food and rent, if we don't see each other much. She said that her parents say I am completely welcome. I would really like to give them some money towards my stay, but she told me they won't accept any. She thinks it's silly for me to stay in the apartment. I would be working, and otherwise I would stay completely out of their way, and I would do any sort of chores to help them. But still, I don't know what to do. I am going there to work, and I felt that I wasn't their responsibility, and that I should be paying for my own place. It is also since I have already stayed there several times for a long time period. What would others do here? Thanks in advance

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