Never used anything but DVD-R and DVD-RAM in my Panasonics.
However - according to this website the DVD-RW discs behave like a CD-RW. You must erase the entire disc and start over again. Only the DVD+RW discs can be edited like DVD-RAM. Perhaps you would be better off sticking with DVD-RAM - I don't think the Panasonics fare well with DVD+RW.
DVD-R use a different dye than DVD+/-RW and with DVD-R the recording is fixed. You can NOT edit out adverts after recording. Only erase the entire programme, and if you ERASE then the space erased cannot be re-used.
To do it you would need to use partial erase and the manual implies that this is a RAM only function.
I believe whole title erasure is possible, so I dont know whether a possible workaround would be splitting titles up into programme segments and adverts , then erasing the ads... but it would be cumbersome and messy.