installing a britax RFing in the 2012 odyssey

[sal799]

so i am going to switch my seats- this is our lineup. 4.5 yo in a securekid 300, and theni have a britax roundabout and a britax marathon. i have a 2 yo and a 11 mo,dont care who sits in what, except for ease of install.
the baby is going to go RFing behind the drivers seat. which is easier to put htere, the marathon or roundabout? does it make a difference?
also- where do i tether too? was looking today, couldn't find anything.